The batteries fijdor mentions are Tesla. They are very powerful and will give a good start every time. The company he and I flew them for (different roles but whatever) also got a new place to overhaul the starters. we were suffering from starter failures quite often and usually carried a spare for our work in the arctic. The Tesla batteries allows you to just pluc an extension cord into the side of the machine to charge the batteries, and also allows a self heater system if needed (it was were I worked 6 months of the year...)